Pour 2 cups water and 1 cup of vinegar into a spray bottle.
Expose the area of the spa cover that contains the mold or mildew.
Spray the vinegar solution directly onto the spa cover, covering the entire area of mold or mildew with a thick coating of the cleaner. Let it sit for 2 minutes.
Scrub the mold off with a cleaning cloth. Continue this procedure until all mold and mildew has been removed.
Wipe the area with a damp cleaning cloth when finished to remove any leftover cleaning solution.